Method of manufacturing printed wiring board

ABSTRACT

A solder resist comprising a thermosetting resin is printed on a surface of an insulating board ( 7 ) having a conductor circuit ( 6 ). The solder resist is then heat-cured to form an insulating film ( 1 ) having a low thermal expansion coefficient. A laser beam ( 2 ) is then applied to the portion of the insulating film in which an opening is to be formed, to burn off the same portion for forming an opening ( 10 ), whereby the conductor circuit ( 6 ) is exposed. This opening may be formed as a hole for conduction by forming a metal plating film on an inner surface thereof. It is preferable that an external connecting pad be formed so as to cover the opening. The film of coating of a metal is formed by using an electric plating lead, which is preferably cut off by a laser beam after the electric plating has finished.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional and claims the benefit of priorityunder 35 U.S.C. §120 from U.S. application Ser. No. 11/260,077, filedOct. 27, 2005, the entire contents of this application is incorporatedherein by reference. U.S. application Ser. No. 11/260,077 is adivisional of U.S. application Ser. No. 10/408,588, filed Apr. 7, 2003,which is a divisional of U.S. application Ser. No. 09/891,819, filedJun. 26, 2001, which is a divisional of U.S. application Ser. No.09/348,935, filed Jul. 7, 1999, which is national stage of InternationalApplication PCT/JP98/00007 filed Jan. 5, 1998 and claims the benefit ofpriority under 35 U.S.C. §119 of Japanese Patent Application Nos.09-361961, 09-065509, 09-062131, 09-052481, and 09-014635 filedrespectively on Dec. 9, 1997, Mar. 3, 1997, Feb. 28, 1997, Feb. 19,1997, and Jan. 10, 1997.

BRACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a printed wiring board and itsmanufacturing method, and particularly relates to a printed wiring boardcapable of forming a very small opening portion and a hole forconductivity and be mounted at high density, an electric conductingmethod between upper and lower faces of an insulating substrate,electric connection of a pad for external connection and the hole forconductivity, and a plating lead used in electric plating.

2. Background Art

As shown in FIGS. 28 and 29, conventionally there is a printed wiringboard having a mounting portion 970 for mounting electronic parts to aninsulating substrate 97 and a conductor circuit 96 arranged around thismounting portion 970. A bonding pad portion 969 forming an end tip ofthe conductor circuit 96 is formed near the mounting portion 970. A padportion 961 for joining a soldering ball, etc. is formed in theconductor circuit 96.

The mounting portion 970 is constructed by a concave portion surroundedby a mounting hole 971 formed in the insulating substrate 97 and a heatradiating plate 98 covering one end of the mounting hole 971.

As shown in FIG. 29, a surface of the insulating substrate 97 is coveredwith an insulating film 91 except for the pad portion 961 and thebonding pad portion 969. In other words, this insulating film 91 exposesthe pad portion 961 and the bonding pad portion 969 by arranging anopening portion 910 above the pad portion 961 and the bonding padportion 969.

A manufacturing method of the above printed wiring board will beexplained next.

First, as shown in FIG. 30, a mounting hole 971 is bored in aninsulating substrate 97 which is sticking a copper foil thereto. Next,the copper foil is etched so that a conductor circuit 96 having a padportion 961 and a bonding pad portion 969 is formed.

Next, as shown in FIG. 28, solder resist constructed by thermosettingresin is printed on a surface of the insulating substrate 97. At thistime, surfaces of the above pad portion 961 and the bonding pad portion962 are exposed as they are without the solder resist printing.

Next, the solder resist is thermally cured and is set to an insulatingfilm 91.

Thereafter, a heat radiating plate 98 is adhered to the surface of theinsulating substrate 97 by using an adhesive 981 so as to cover one endof the mounting hole 971.

Thus, a printed wiring board 9 is obtained.

However, the above conventional manufacturing method of the printedwiring board 9 has the following problems.

Specifically, as shown in FIG. 31, except for a portion of the padportion 961 no very small opening portion 910 can be formed in theinsulating film 91 in a method for partially printing the above solderresist. Therefore, it is impossible only to expose a very small portionin the conductor circuit 96. As a result, no high density mounting canbe improved.

In contrast to this, a manufacturing method as shown in FIG. 32 isproposed. In this method, an entire surface of the insulating substrate97 forming the conductor circuit 96 therein is covered with a solderresist 912 constructed by an optical curing type resin. The solderresist 912 is exposed in a state in which a light interrupting mask 94is arranged above an opening portion forming portion.

In this method, the solder resist 912 in a portion of light 940interrupted by the mask 94 is not cured and is left as it is. In thisstate, the solder resist in an exposed portion is cured and forms aninsulating film. Next, the insulating substrate 97 is dipped into adeveloping liquid and the solder resist in an uncured portion is removedfrom the insulating substrate 97. Thus, an opening portion 910 is formedin the cured insulating film 91 and one portion of the conductor circuit96 is exposed.

However, in this method, since the optical curing type resin used as thesolder resist has a property of absorbing humidity, no solder resist issuitable as the insulating film.

Further, since the above light has scattering light, the above lightcannot be sufficiently interrupted so that no opening portion 910 can beformed in a sharp state. Therefore, for example, it is almost impossibleto form a very small opening portion having a size equal to or smallerthan 0.60 mm. Therefore, no high density mounting can be improved.

By using a drill there is also the method for boring a hole forconductivity. However, in this case, it is also difficult to form a verysmall hole for conductivity.

Further, there is a case in which various kinds of conductive membersare formed around the hole for conductivity. Tangibly, such conductivemembers are constructed by a land surrounding a peripheral portion ofthe hole for conductivity, a pad for externally joining a solderingball, a plating lead for forming electric plating, etc. High density isalso desirable when these conductive members are formed.

With consideration to such conventional problems, the present inventionprovides a printed wiring board able to form an insulating film having avery small opening portion and be mounted at high density, and amanufacturing method of the printed wiring board.

BRIEF SUMMARY OF INVENTION

A first invention is a manufacturing method of a printed wiring boardcharacterized in that a conductor circuit is formed on the surface of aninsulating substrate;

a solder resist made of thermosetting resin is next printed on thesurface of said insulating substrate;

an insulating film having a coefficient thermal expansion equal to orsmaller than 100 ppm/° C. is next formed by thermally curing the solderresist; and

the conductor circuit is next exposed by irradiating a laser beam to anopening portion forming portion in the insulating film and burning-outthe insulating film of said opening portion forming portion and formingan opening portion.

An operation and effects of the first invention will be explained.

In the first invention, the entire surface of the insulating substrateis covered with the insulating film and the laser beam is irradiated toa portion for forming the opening portion. High energy is given by alaser to the irradiating portion of the laser beam so that thisirradiating portion has a very high temperature and is burnt out.Therefore, a very small opening portion can be formed in the insulatingfilm.

Further, no light is scattered since the laser beam is parallel light.Therefore, a very small opening portion having an approximately sizefrom 0.05 to 0.60 mm can be formed in desirable position and size.Accordingly, many opening portions can be formed in a small space sothat high density mounting can be realized.

Thermosetting resin used in the solder resist has a low coefficientthermal expansion equal to or smaller than 100 ppm/° C. Therefore, thethermosetting resin has a property in which generation of stress of thesolder resist is reduced by a temperature cycle test, etc. Accordingly,a close attaching property of the solder resist and the conductorcircuit is improved.

In contrast to this, when the coefficient thermal expansion exceeds 100ppm/° C., a problem exists in that the stress of the solder resist isincreased by the temperature cycle test, etc.

A lower limit of the coefficient thermal expansion of the thermosettingresin includes 0 ppm/° C., but is preferably set to 1 ppm/° C. to moreeffectively show the above effects of the present invention.

The coefficient thermal expansion of the thermosetting resin used in thesolder resist is preferably further set to range from 30 to 50 ppm/° C.

The above solder resist is preferably constructed by epoxy resin,triazine resin, polyimide resin, or a modified material thereof. In thiscase, a heat resisting close attaching property is improved between thesolder resist and the conductor circuit. Further, an insulatingsubstrate having a low water absorbing ratio is obtained through thermalcuring of the solder resist.

A metallic plating film is preferably formed on a surface of the exposedconductor circuit after the laser beam is irradiated to the openingportion forming portion in the above insulating film. In this case, asolder leaking property on the conductor circuit surface is improved.Further, corrosion of the conductor circuit can be prevented.

Desmear processing is preferably performed on the surface of the exposedconductor circuit after the irradiation of said laser beam. The desmearprocessing is the processing for dissolving and removing the residue ofthe solder resist left on the surface of the exposed conductor circuitby a drug. In this case, the surface of the exposed conductor circuit iswashed so that adhesive strength of the metallic plating film isimproved. For example, the drug for the desmear processing isconstructed by concentrated sulfuric acid, chromic acid, both of thesemixed acid, or an acid obtained by adding sodium permanganate andpotassium permanganate to each of these acids.

When the desmear processing is performed, there is a case in which theinsulating film is separated from the insulating substrate on aninterface with this insulating substrate at a peripheral edge of theopening portion in accordance with a kind of the solder resist formingthe insulating film. Therefore, when the desmear processing isperformed, the above solder resist is preferably constructed bythermosetting resin. The thermosetting resin has a resisting propertywith respect to a strong acid used in the desmear processing. Therefore,the separation of the insulating film at the peripheral edge of theopening portion can be prevented by using the thermosetting resin as thesolder resist. For example, this thermosetting resin is constructed byepoxy resin, polyimide resin, triazine resin, etc.

A second invention is a printed wiring board characterized in that anupper face pattern is formed on an upper face of an insulating substrateand a lower face pattern is formed on a lower face of said insulatingsubstrate and a hole for conductivity extends through said insulatingsubstrate and reaches an upper face of said lower face pattern, and ametallic filling material filled with a metal for electricallyconducting said upper face pattern and said lower face pattern isarranged within the hole for conductivity; and said upper face patternhas a width from 0.05 to 0.2 mm around said hole for conductivity.

In the second invention, it is most noticeable that the metallic fillingmaterial for electrically conducting the upper face pattern and thelower face pattern is arranged within the hole for conductivity.

An operation and effects of the second invention will be explained.

The hole for conductivity extends through the insulating substrate and alower end portion of the hole for conductivity is closed by the lowerface pattern. In contrast to this, the upper face pattern is arrangedaround an upper end portion of the hole for conductivity. Therefore, theupper face pattern and the lower face pattern can be electricallyconducted to each other through the metallic filling material by formingthe metallic filling material within the hole for conductivity.

The metallic filling material within the hole for conductivity is joinedto the upper face pattern at least on a side face of an upper endportion of the metallic filling material. Therefore, the upper facepattern can be joined to the metallic filling material irrespective ofthe large or small value of a width of the upper face pattern, and theupper face pattern and the hole for conductivity can be electricallyconducted reliably.

Therefore, it is not necessary that the width of a plating attachingarea for forming a plating film in the hole for conductivity is formedin the upper face pattern as in the conventional case. Consequently, inaccordance with the present invention, the width of the upper facepattern arranged around the hole for conductivity can be reduced to awidth of 0.05 to 0.2 mm. Further, a surplus area is formed on a surfaceof the insulating substrate by the reduction in the width of the upperface pattern. Accordingly, another upper face pattern, an electronicpart mounting portion, etc. can be further formed in this surplus areaso that high density mounting can be achieved.

The second invention can also be applied to a multilayer printed wiringboard having two or more insulating substrates laminated to each otheras well as the printed wiring board constructed by a single insulatingsubstrate. In the case of the multilayer printed wiring board, the holefor conductivity for electrically conducting the upper face pattern andthe lower face pattern can be arranged such that this hole forconductivity extends through each insulating substrate. Further, thishole for conductivity can also be arranged such that this holecontinuously extends through plural insulating substrates. In themultilayer printed wiring board, there is a case in which the upper facepattern or the lower face pattern is set to an inner layer pattern andis also set to an outer layer pattern.

The above metallic filling material is preferably constructed by solder.In this case, the interior of the hole for conductivity is easily filledwith the solder since the solder is melted at a low temperature.Further, the joining can be performed at low cost since the solderingmaterial is cheap.

The above metallic filling material is preferably constructed by aplating deposit material in which a plating layer is deposited on theabove lower face pattern within the above hole for conductivity. In theplating deposit material, the metallic filling material is formed withinthe hole for conductivity by sequentially depositing a metal from anupper face of the lower face pattern within the hole for conductivityand/or a wall face of the hole for conductivity. Thus, the metallicfilling material can be easily formed within the hole for conductivity.

In particular, the plating deposit material is preferably formed byusing an electric plating method. This is because the metallic fillingmaterial can be rapidly formed since the depositing speed of a metal inthe electric plating method is higher than that in a chemical platingmethod. In particular, the electric plating method is preferably usedwhen the insulating substrate is thin in thickness and the hole forconductivity is shallow in depth. This is because the metallic fillingmaterial can be rapidly formed since a depositing thickness from theupper face of the lower face pattern may be set to be thin.

The above upper face pattern is preferably covered with a resist filmexcept for a peripheral portion of the above hole for conductivity. Inthis case, the interior of the hole for conductivity can be filled withthe metal without attaching the metal for forming the metallic fillingmaterial to the upper face pattern near the peripheral portion of thehole for conductivity.

As a method for manufacturing the printed wiring board as the secondinvention, there is a manufacturing method of a printed wiring boardcharacterized by an upper face pattern formed on an upper face of aninsulating substrate around a forming portion of a hole for conductivityso as to surround this forming portion of the hole for conductivity, anda lower face pattern is formed on a lower face of said insulatingsubstrate so as to cover said forming portion of the hole forconductivity; the hole for conductivity extending through saidinsulating substrate and reaching an upper face of said lower facepattern is next formed in the forming portion of the hole forconductivity in said insulating substrate; and a metallic fillingmaterial is next formed by filling the interior of said hole forconductivity with a metal so that said upper face pattern and said lowerface pattern are electrically conducted to each other through themetallic filling material.

In this manufacturing method, after the upper face pattern and the lowerface pattern are formed in the insulating substrate, the metallicfilling material is formed within the hole for conductivity in a statein which the hole for conductivity is set to a non-through hole bycovering a lower end of the hole for conductivity with the lower facepattern. Therefore, the upper face pattern and the lower face patterncan be conducted to each other electrically through the metallic fillingmaterial.

Further, since the electric conduction is performed by the metallicfilling material formed within the hole for conductivity, it is notnecessary that the width of a plating attaching area for forming aplating film in the hole for conductivity is formed in the upper facepattern. Accordingly, the width of the upper face pattern arrangedaround the hole for conductivity can be reduced in comparison with theconventional case. Therefore, an upper face pattern, an electronic partmounting portion, etc. can be formed by the reduction in the width ofthe upper face pattern so that high density mounting can be achieved.

When the above hole for conductivity is formed, a laser beam ispreferably irradiated to the forming portion of the hole forconductivity in the insulating substrate. In this case, the hole forconductivity as a non-through hole can be easily formed in the formingportion of the hole for conductivity.

In particular, the hole for conductivity having a small diameter can beaccurately formed since the laser beam can bore the hole locally.

Before the interior of the above hole for conductivity is filled withthe metal, the upper face of the above insulating substrate ispreferably covered with a resist film except for the above hole forconductivity. In this case, when the interior of the hole forconductivity is filled with the metal, no upper face pattern is stainedby attaching the metal to this upper race pattern, etc.

The metal filling the interior of the above hole for conductivity isconstructed preferably by solder. It is also preferable to fill theinterior of the above hole with the metal by depositing a plating layeron the upper face of the above lower face pattern within the above holefor conductivity. In these cases, as mentioned above, the interior ofthe hole for conductivity can be easily filled with the metal.

The second invention can be utilized in a multilayer printed wiringboard requiring high connection reliability such as a memory module, amultichip module, a mother board, a daughter board, a plastic package,etc.

A third invention is a printed wiring board having an insulatingsubstrate constructed by one, two or more insulating layers, a pad forexternal connection arranged in an outermost layer of the insulatingsubstrate, a conductor pattern arranged in another layer different fromsaid outermost layer, and a hole for conductivity for electricallyconnecting said pad for external connection and said conductor pattern;the printed wiring board characterized with said pad for externalconnection closing an opening portion of the hole for conductivity onits outermost layer side forming a bottom portion of the hole forconductivity, and a metallic plating film for continuously covering aninner wall and the bottom portion of the hole for conductivity is formedwithin said hole for conductivity.

An operation and effects of the third invention will be explained.

The pad for external connection is arranged so as to form the bottomportion of the hole for conductivity. Therefore, it is not necessary toform a conductor pattern for connecting the hole for conductivity andthe pad for external connection. Accordingly, a surplus area is formedon a surface of the insulating substrate and another conductor pattern,etc. can be further formed in this surplus area so that high densitysurface mounting can be obtained. Further, the distance betweenrespective holes for conductivity can be reduced so that the holes forconductivity can be formed at high density.

The pad for external connection closes the opening portion of the holefor conductivity on its outermost layer side and forms the bottomportion of the hole for conductivity. Therefore, the pad for externalconnection has at least one area of the opening portion of the hole forconductivity. Hence, the pad for external connection can secure asufficient joining area for joining an external connecting terminal andhas an excellent joining strength to the external connecting terminal.

The metallic plating film for continuously covering the inner wall andthe bottom portion of the hole for conductivity is arranged within thehole for conductivity. Therefore, the bottom portion of the pad forexternal connection is strongly joined to the metallic plating film sothat joining strength to the hole for conductivity is improved. Hence,for conductivity the pad for external connection can be reduced to asize close to that of the opening portion of the hole.

Accordingly, it is possible to realize high density mounting of the padfor external connection and increase density of surface mounting of theinsulating substrate.

For example, the above conductor pattern is all conductive patternswhich are able to be formed on the surface of the insulating substratesuch as a wiring circuit, a pad, a terminal, a land, etc. For example,the conductor pattern is formed from etching of a metallic foil,metallic plating, etc.

The above insulating layer is constructed from a synthetic resin simplesubstance, a resin basic material constructed by synthetic resin and aninorganic filler, a cloth basic material constructed by synthetic resinand an inorganic cloth, a prepreg, etc. The above synthetic resin isconstructed by epoxy resin, phenol resin, polyimide resin, polybutadieneresin, fluoride resin, etc.

The third invention can be utilized in a multilayer printed wiring boardrequiring high connection reliability such as a memory module, amultichip module, a mother board, a daughter board, a plastic package,etc.

An external connecting terminal is preferably joined to a surface of theabove pad for external connection in a central position of the hole forconductivity. In this case, the external connecting terminal can bestably joined to the surface of the pad for external connection.

The above external connecting terminal is preferably constructed by asoldering ball, a probe, conductive paste or a conductive wire. This isbecause these external connecting terminals can exactly input and outputelectric information transmitted to the pad for external connection.

When the printed wiring board of the above third invention ismanufactured, there is a manufacturing method of a printed wiring boardin which a conductor pattern is formed on an upper face of an insulatinglayer and a pad for external connection is formed on a lower face of theinsulating layer, and said conductor pattern and the pad for externalconnection are electrically connected to each other by a hole forconductivity; the manufacturing method being characterized by an upperface copper foil and a lower face copper foil which are firstrespectively stuck to the upper and lower faces of the insulating layer;an opening hole is next formed by removing a portion corresponding to aforming portion of the hole for conductivity in said upper face copperfoil by etching; the hole for conductivity is next formed in theinsulating layer exposed from the opening hole of said upper face copperfoil, and a bottom portion of the hole for conductivity is set to reachsaid lower face copper foil; a chemical plating film is next formed inan inner wall of the hole for conductivity; an electric plating film forcontinuously covering the inner wall and the bottom portion of the holefor conductivity is next formed within the hole for conductivity; aconductor pattern electrically connected to said hole for conductivityis next formed from the upper face copper foil from etching said upperface copper foil and the lower face copper foil, and a pad for externalconnection for closing an opening portion of said hole for conductivityis formed from said lower face copper foil.

In this manufacturing method, it is most noticeable that the pad forexternal connection is formed from etching the lower face copper foilconstituting the bottom portion of the hole for conductivity after thehole for conductivity is formed and the inner wall and the bottomportion of the hole for conductivity are covered with the metallicplating film.

After the bottom portion of the hole for conductivity is formed in orderto reach the lower face copper foil, the electric plating film forcontinuously covering the inner wall and the bottom portion of the holefor conductivity is formed in the hole for conductivity. The electricplating film is closely attached to the lower face copper foil as thebottom portion of the hole for conductivity. Therefore, the pad forexternal connection can be securely closely attached to the electricplating film within the hole for conductivity even when the pad forexternal connection is reduced to a size approximately similar to thatof the hole for conductivity from etching the lower face copper foil.

Therefore, a surplus area is formed on the lower face of the insulatinglayer by reducing the size of the pad for external connection. Anotherpad for external connection, a conductive layer, etc. can be furthermounted to this surplus area at high density.

For example, there is a method for irradiating a laser beam to theforming portion of the hole for conductivity in the insulating layer asa method for forming the hole for conductivity in the above insulatinglayer.

The laser beam sequentially bores a hole within the insulating layer bygiving high energy to the insulating layer. The laser beam is reflectedon the lower face copper foil when an end tip of the laser beam reachesthe lower face copper foil. Therefore, when the irradiation of the laserbeam is stopped here, a non-through hole for conductivity having oneopening portion covered with the lower face copper foil is formed.

It is noticeable here that the non-through hole reaching the lower facecopper foil can be formed by irradiating the laser beam. Conventionallyit is necessary that a hole is bored in the insulating layer by a drilland a router and an opening portion of this hole is then covered with acopper foil to form such a non-through hole. However, the non-throughhole reaching the lower face copper foil can be formed by irradiatingthe laser beam so that no covering work of the opening portion isrequired after the boring. Therefore, the number of manufacturingprocesses is reduced and manufacturing cost can be reduced.

The conductor pattern formed on the upper surface of the insulatinglayer, and the pad for external connection formed on the lower face ofthe insulating layer can be simultaneously formed by etching the upperface copper foil and the lower face copper foil. Accordingly, theprinted wiring board can be manufactured efficiently and easily.

After the above conductor pattern and the pad for external connectionare formed, one, two or more other insulating layers are preferablylaminated with the above insulating layer having the pad for externalconnection in a state in which the above pad for external connection isarranged in an outermost layer. In this case, high density mounting ofthe printed wiring board can be obtained.

An external connecting terminal is preferably joined to a surface of theabove pad for external connection in a central position of the hole forconductivity. In this case, similar to the above-mentioned invention ofclaim 2, the external connecting terminal can be joined to the pad forexternal connection in a stable state.

A fourth invention is a manufacturing method of a printed wiring boardhaving a conductor pattern covered with an electric plating film on thesurface of an insulating substrate; the manufacturing method beingcharacterized in that the manufacturing method comprises a process forforming the conductor pattern on the surface of the insulating substrateand forming a plating lead electrically connected to the conductorpattern; a process for covering a surface of the conductor pattern withthe electric plating film by flowing an electric current to theconductor pattern through said plating lead; and a process for meltingand cutting the plating lead by irradiating a laser beam to said platinglead.

In the fourth invention, it is most noticeable that the plating lead ismelted and cut by the laser beam after the electric plating film isformed on the surface of the conductor pattern by using the platinglead.

An operation and effects of the fourth invention will be explained.

Coherent light having aligned phases is obtained by the laser beam sothat directivity is good. Therefore, high energy can be given to a verysmall portion by irradiating the laser beam. Hence, only the platinglead can be melted and cut without damaging the conductor patternarranged around the plating lead even when the plating lead is finelyconstructed. Accordingly, the plating lead can be formed in a very smallpattern so that the distance between conductor patterns can be reducedto 0.3 mm at its minimum. Accordingly, high density mounting of theconductor patterns can be realized in accordance with the presentinvention.

The above laser beam is preferably constructed by using an excimerlaser, a carbon dioxide gas laser, etc.

The laser beam preferably has energy intensity set such that the platinglead is sufficiently melted and cut and no insulating substrate belowthe plating lead is damaged. For example, such energy intensity is setsuch that a wavelength ranges from 20 nm to 10 μm and an output rangesfrom 30 to 300 W and an irradiating time ranges from 0.1 to 1.0 second.

A melting and cutting state of the plating lead using the laser beam isadjusted by the energy intensity of the laser beam, the irradiatingtime, etc.

The above electric plating film can be formed by a general electricplating method. For example, the electric plating film can be formed bydepositing a metal on the surface of the conductor pattern by flowing anelectric current to the conductor pattern through the plating lead in astate in which the insulating substrate is dipped into an electricplating reservoir.

For example, the above conductor pattern is all conductive patterns ableto be formed on the surface of the insulating substrate such as a wiringcircuit, a pad, a terminal, a land, etc. For example, the conductorpattern is formed by etching of a metallic foil, metallic plating, etc.

The above insulating substrate is constructed by a synthetic resinsimple substance, a resin basic material constructed by synthetic resinand an inorganic filler, a cloth basic material constructed by syntheticresin and an inorganic cloth, etc. The above synthetic resin isconstructed by epoxy resin, phenol resin, polyimide resin, polybutadieneresin, fluoride resin, etc. These insulating substrates can be laminatedwith other insulating substrates by interposing an adhesive such as aprepreg, etc. so that a multilayer printed wiring board can beconstructed.

There is a manufacturing method of the printed wiring board for formingthe electric plating film in an inner wall of the through hole inaddition to the surface of the conductor pattern by utilizing the abovefourth invention. This manufacturing method is a manufacturing method ofa printed wiring board in which the printed wiring board has a conductorpattern formed on the surface of an insulating substrate and also has athrough hole extending through said insulating substrate, and a surfaceof said conductor pattern and an inner wall of the through hole arecovered with an electric plating film; the manufacturing method beingcharacterized in that the manufacturing method comprises a process forboring the through hole in the insulating substrate; a process forforming a chemical plating film in the inner wall of said through hole;a process for forming the conductor pattern on the surface of saidinsulating substrate, and forming a plating lead for electricallyconnecting the conductor pattern and said chemical plating film withinthe through hole; a process for covering surfaces of the conductorpattern and said chemical plating film with the electric plating film byflowing an electric current to the conductor pattern and said chemicalplating film through said plating lead; and a process for melting andcutting the plating lead by irradiating a laser beam to said platinglead.

When the electric plating film is formed in the inner wall of thethrough hole, the chemical plating film is formed by the chemicalplating method in this inner wall after the through hole is bored. Thus,conductivity is given to the inner wall of the through hole. An electriccurrent is flowed to the chemical plating film covering the inner wallof the through hole through the plating lead in a state in which theinsulating substrate is dipped into an electric plating reservoir. Thus,a metal is deposited on the surface of the chemical plating film so thatthe electric plating film is formed.

Similar to the above fourth invention, the plating lead connected to thethrough hole and the conductor pattern is also melted and cut byirradiating the laser beam in this manufacturing method after theelectric plating film is formed. Therefore, the plating lead can be setto a very small portion so that both of distances between through holesand between the conductor patterns can be reduced to about 0.3 mm at itsminimum. Accordingly, high density mounting of the through holes and theconductor patterns can be realized.

The above through hole is a through hole extending through theinsulating substrate, or a non-through hole not extending through theinsulating substrate.

The above chemical plating film can be formed by the general chemicalplating method.

Further, similar to the above case, the electric plating film can beformed on the surface of the conductor pattern by the general electricplating method.

The above laser beam can be constructed by using an excimer laser, acarbon dioxide gas laser, etc.

The process for forming the above conductor pattern and the plating leadmay be performed before or after the boring process of the through hole.Otherwise, the process for forming the above conductor pattern and theplating lead may be also performed before or after the forming processof the above chemical plating film.

The printed wiring board of the fourth invention can be utilized in amultilayer printed wiring board requiring high connection reliabilitysuch as a memory module, a multichip module, a mother board, a daughterboard, a plastic package, etc.

A more detailed description of the invention is provided in thefollowing description and appended claims taken in conjunction with theaccompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1( a) is a cross-sectional view of an insulating substrate coveredwith an insulating film in an embodiment mode example 1, and FIG. 1( b)is a cross-sectional view of the insulating substrate showing a methodfor forming an opening portion in the insulating film.

FIG. 2 is a cross-sectional view of the insulating substrate in which aplating film is formed on the surface of a conductor circuit in theembodiment mode example 1.

FIG. 3( a) is a cross-sectional view of the insulating substrate forshowing an opening portion opened in the same shape approximately as theconductor circuit in the embodiment mode example 1, and FIG. 3( b) is across-sectional view of the insulating substrate for showing an openingportion opened until a peripheral edge of the conductor circuit.

FIG. 4 is a cross-sectional view of a printed wiring board in anembodiment mode example 2.

FIG. 5 is an explanatory view showing a peripheral portion of an upperend of a hole for conductivity in the embodiment mode example 2.

FIG. 6 is an explanatory view showing a forming method of the hole forconductivity in the embodiment mode example 2.

FIG. 7 is an explanatory view of the insulating substrate forming thehole for conductivity therein in the embodiment mode example 2.

FIG. 8 is a cross-sectional view of a printed wiring board in anembodiment mode example 4.

FIG. 9 is a cross-sectional view of a main portion of the printed wiringboard in the embodiment mode example 4.

FIG. 10 is an explanatory view for showing a manufacturing method of theprinted wiring board in the embodiment mode example 4 and an insulatinglayer sticking a copper foil thereto.

FIG. 11 is an explanatory view of the insulating layer continued fromFIG. 10 and showing a forming method of a hole for conductivity.

FIG. 12 is an explanatory view continued from FIG. 11 and showing theinsulating layer forming the hole for conductivity therein.

FIG. 13 is an explanatory view continued from FIG. 12 and showing theinsulating layer in which a metallic plating film is formed within thehole for conductivity.

FIG. 14 is an explanatory view continued from FIG. 13 showing theinsulating layer in which a conductor pattern and a pad for externalconnection are formed.

FIG. 15 is a rear explanatory view of the insulating substrate showingan arranging position of the pad for external connection in theembodiment mode example 4.

FIG. 16 is a cross-sectional view of the printed wiring board used as achip size package in the embodiment mode example 4.

FIG. 17 is a cross-sectional view of a printed wiring board in anembodiment mode example 5.

FIG. 18 is a cross-sectional view of a printed wiring board in anembodiment mode example 6.

FIG. 19 is a plan view of the printed wiring board in the embodimentmode example 6.

FIG. 20 is a rear view of the printed wiring board in the embodimentmode example 6.

FIG. 21 is a sectional explanatory view of an insulating substratesticking a copper foil thereto in a manufacturing method of the printedwiring board in the embodiment mode example 6.

FIG. 22 is a sectional explanatory view continued from FIG. 21 showingthe insulating substrate in which a conductor pattern and a plating leadare formed.

FIG. 23 is a sectional explanatory view continued from FIG. 22 showingthe insulating substrate in which a through hole and a chemical platingfilm are formed.

FIG. 24 is a sectional explanatory view continued from FIG. 23 showingthe insulating substrate forming an electric plating film therein.

FIG. 25 is a plan explanatory view continued from FIG. 23 showing theinsulating substrate forming the electric plating film therein.

FIG. 26 is a sectional explanatory view continued from FIG. 25 showing amelting and cutting method of the plating lead.

FIG. 27 is a sectional explanatory view continued from FIG. 26 showingthe insulating substrate removing the plating lead therefrom.

FIG. 28 is a cross-sectional view of a printed wiring board in aconventional example.

FIG. 29 is a partial plan view of the printed wiring board in theconventional example.

FIG. 30 is a cross-sectional view of an insulating substrate forming aconductor circuit therein in the conventional example.

FIG. 31 is a cross-sectional view of the insulating substrate in which asolder resist is printed in the conventional example.

FIG. 32 is a cross-sectional view of an insulating substrate showing amethod for forming an opening portion in an insulating film in anotherconventional example.

FIG. 33 is a cross-sectional view of the insulating substrate formingthe opening portion in the insulating film in another conventionalexample.

EXPLANATION OF REFERENCE NUMERALS

-   101 - - - insulating film,-   110 - - - opening portion,-   102 - - - laser beam,-   106 - - - conductor circuit,-   107 - - - insulating substrate,-   201 - - - upper face pattern,-   202 - - - lower face pattern,-   203 - - - hole for conductivity,-   205 - - - metallic filling material,-   261, 262 - - - resist film,-   207 - - - insulating substrate,-   208 - - - printed wiring board,-   301 - - - pad for external connection,-   310 - - - external connecting terminal,-   321 - - - upper face copper foil,-   322 - - - lower face copper foil,-   323 - - - metallic plating film,-   325, 326 - - - conductor pattern,-   327 - - - bonding pad,-   331, 332 - - - hole for conductivity,-   341, 342 - - - printed wiring board,-   305 - - - insulating substrate,-   351, 352 - - - insulating layer,-   306 - - - solder resist,-   307 - - - electronic part,-   370 - - - mounting portion,-   308 - - - partner member,-   401 - - - conductor pattern,-   402 - - - plating lead,-   403 - - - printed wiring board,-   404 - - - electric current,-   405 - - - through hole,-   406 - - - mounting portion,-   407 - - - insulating substrate,-   408 - - - laser beam.

DETAILED DESCRIPTION OF THE INVENTION

The following is a detailed description and explanation of the preferredembodiments and best modes for embodying the invention along with someexamples thereof.

Embodiment Mode Example 1

A manufacturing method of a printed wiring board in an embodiment modeexample of a first invention will be explained by using FIGS. 1 to 3.

A summary of this manufacturing method will first be explained. That is,a solder resist constructed by thermosetting resin is printed on thesurface of an insulating substrate 107 having a conductor circuit 106and including a surface of this conductor circuit 106. The solder resistis thermally cured so that an insulating film 101 having a lowcoefficient of thermal expansion is formed (FIG. 1( a)). Next, a laserbeam 102 is irradiated to an opening portion forming portion in theinsulating film 101 and this opening portion forming portion is burntout, and an opening portion 110 is formed and one portion of theconductor circuit 106 is exposed (FIG. 1( b)).

A manufacturing method of the above printed wiring board will next beexplained in detail.

First, a copper foil having 18 μm in thickness is stuck to an insulatingsubstrate constructed by resin including glass epoxy. Next, a hole formounting electronic parts (see FIG. 28) is bored into the insulatingsubstrate 107. Next, as shown in FIG. 1( a), the copper foil is etchedand a conductor circuit 106 is formed on a surface of the insulatingsubstrate 107.

Next, a solder resist constructed by thermosetting resin is printed onthe entire surface of the insulating substrate 107. Epoxy-includingresin impregnated with a filler is used as the thermosetting resin. Theprinted solder resist has 40 μm in thickness.

Next, the insulating substrate 107 is put into a heating furnace and thesolder resist is thermally cured and set to an insulating film 101 (FIG.1( a)). This insulating film 101 has a low coefficient thermal expansionof 50 ppm/° C.

Next, a laser beam 102 is irradiated to an opening portion formingportion in the insulating film 101 and this opening portion formingportion is burnt out. As shown in FIG. 1( b), an opening portion 110 isthus formed in the insulating film 101. The laser is constructed byusing a general CO₂ laser.

Thus, a conductor circuit 106 is exposed from the opening portion 110.

Next, desmear processing is performed with respect to the conductorcircuit 106 by using a drug in which permanganate or bichromate isdissolved into a strong acid such as concentrated sulfuric acid, etc.

Next, as shown in FIG. 2, a Ni—Au plating film 131 is formed by anelectric plating method on a surface of the exposed conductor circuit106. Next, an Au plating film 132 is formed on a surface of the Ni—Auplating film 131 by the electric plating method.

Thereafter, a heat radiating plate is adhered to a surface of theinsulating substrate 107 by using an adhesive so that a printed wiringboard is obtained (see FIG. 28).

As shown in FIG. 1( b), the opening portion 110 formed by irradiatingthe laser beam may be constructed such that only one portion of an upperface of the conductor circuit 106 is exposed. However, as shown in FIG.3, the opening portion 110 may also be constructed such that one portion(FIG. 3( a)) of the upper face and a side face of the conductor circuit106, or the conductor circuit 106 and the insulating substrate 107 at aperipheral edge of this conductor circuit 106 are exposed.

An operation and effects of this example will next be explained.

In this example, as shown in FIG. 1( b), the entire surface of theinsulating substrate 107 is covered with the insulating film 101 and thelaser beam 102 is irradiated to a portion for forming the openingportion. High energy is given by the laser beam 102 to the irradiatingportion of the laser beam 102 so that the irradiating portion has a veryhigh temperature and is burnt out. Therefore, a very small openingportion 110 can be formed in the insulating film 101.

Further, no light is scattered since the irradiated laser beam isparallel light. Therefore, a very small opening portion having about0.05 to 0.60 mm in size can be formed in a desirable position and size.

Accordingly, many opening portions can be formed in a small space andhigh density mounting can be obtained.

The insulating film 101 is constructed by thermosetting epoxy resin.Therefore, as shown in FIG. 1( b), no insulating film 101 is separatedfrom the insulating substrate 107 at a peripheral edge 108 of theopening portion 110 by the desmear processing.

Embodiment Mode Example 2

A printed wiring board in an embodiment mode example of a secondinvention will be explained by using FIGS. 4 to 7.

As shown in FIG. 4, the printed wiring board 208 in this example has anupper face pattern 201 formed on an upper face of an insulatingsubstrate 207, a lower face pattern 202 formed on a lower face of theinsulating substrate 207, and a hole 203 for conductivity extendingthrough the insulating substrate 207 and reaching an upper face 228 ofthe lower face pattern 202. A metallic filling material 205 is arrangedwithin the hole 203 for conductivity and is filled with solder forelectrically conducting the upper face pattern 201 and the lower facepattern 202. The upper face pattern 201 is covered with a resist film261 except for a peripheral portion of the hole 203 for conductivity.

The insulating substrate is set to have 0.1 mm in thickness. As shown inFIG. 5, the hole 203 for conductivity has a diameter A of 0.3 mm. Anupper end portion 231 of the hole 203 for conductivity is surrounded bythe upper face pattern 201 having 0.025 mm in width B. In contrast tothis, a lower end portion 232 of the hole 203 for conductivity iscovered with the lower face pattern 202 so as to cover a bottom portionof the lower end portion 232.

A mounting portion for mounting electronic parts is formed in a centralportion of the printed wiring board 208 (omitted in the drawings).

A manufacturing method of the above printed wiring board will next beexplained.

First, an insulating substrate constructed by glass epoxy resin isprepared. A copper foil is stuck to upper and lower faces of theinsulating substrate. Next, an unnecessary portion of the copper foil isetched and removed from the copper foil. Thus, as shown in FIG. 6, anupper face pattern 201 and a lower face pattern 202 are formed. Theupper face pattern 201 is formed around a forming portion 230 of a holefor conductivity on an upper face of the insulating substrate 207. Thelower face pattern 202 is formed on a lower face of the insulatingsubstrate 207 in order to cover the forming portion 230 of the hole forconductivity.

Next, the upper face of the insulating substrate 207 is covered with aresist film 261. The resist film 261 formed on this upper face forms anopening hole 263 for opening the insulating substrate 207 in the formingportion 230 of the hole for conductivity.

Further, the lower face of the insulating substrate 207 is covered witha resist film 262. The resist film 262 formed on this lower face coversthe lower face of the insulating substrate 207 including the formingportion 230 of the hole for conductivity.

Next, a laser beam 204 is irradiated to the forming portion 230 of thehole for conductivity. A carbon dioxide gas laser is used as a laser ofthe laser beam 204. Thus, as shown in FIG. 7, a hole 203 forconductivity extending through the insulating substrate 207 in theforming portion 230 of the hole for conductivity and reaching an upperface of the lower face pattern 202 is formed in a state in which thelower face pattern 202 is left.

Next, an electric plating method of flowing electricity to the lowerface pattern 202 is executed in a state in which the insulatingsubstrate 207 is dipped into a solder plating reservoir. Thus, as shownin FIG. 4, solder is deposited from the upper face of the lower facepattern 202 within the hole 203 for conductivity, and fills the entireinterior of the hole 203 for conductivity so that a metallic fillingmaterial 205 is formed.

Thus, the above printed wiring board 208 is obtained.

An operation and effects of this example will next be explained.

As shown in FIG. 4, the hole 203 for conductivity is formed so as toextend through the insulating substrate 207 and the metallic fillingmaterial 205 is formed within the hole 203 for conductivity. A lower endportion 232 of the hole 203 for conductivity is covered with the lowerface pattern 202. In contrast to this, the upper face pattern 201 isformed around an upper end portion 31 of the hole 203 for conductivity.Therefore, the upper face pattern 201 and the lower face pattern 202 canbe electrically conducted to each other through the metallic fillingmaterial 205 within the hole 203 for conductivity.

Further, the metallic filling material 205 formed within the hole 203for conductivity is joined to the upper face pattern 201 on a side faceof an upper end portion 231 of this metallic filling material 205.Therefore, the upper face pattern 201 can be joined to the metallicfilling material 205 irrespective of the large or small value width ofthe upper face pattern 201 so that the upper face pattern 201 and themetallic filling material 205 can reliably be electrically conducted toeach other. Accordingly, as in the conventional case it is not necessarythat the width of a plating attaching area for forming a plating film inthe hole 203 for conductivity is formed in the upper face pattern 201.

In accordance with this example, the width of the upper face pattern 201formed around the hole 203 for conductivity can be narrowed incomparison with the conventional case. Further, a surplus area is formedon a surface of the insulating substrate 207 by a narrowed amount of thewidth of the upper face pattern 201. Accordingly, another upper facepattern, an electronic part mounting portion, etc. can be further formedin this surplus area so that high density mounting can be achieved.

Embodiment Mode Example 3

This example is an embodiment mode example of the second invention. Thisexample differs from the embodiment mode example 2 in that the interiorof the hole for conductivity is filled with a metal by a printingmethod.

Specifically, similar to the above embodiment mode example 2, after thehole for conductivity is formed, a mask for printing having an openinghole in a portion corresponding to the hole for conductivity is arrangedon an upper face side of the insulating substrate. Next, soldering pasteis arranged on the mask and is pressed by a roller. Thus, the solderingpaste is moved from the opening hole of the mask into the hole forconductivity. Accordingly, the interior of the hole for conductivity isfilled with the solder so that a metallic filling material is formed.

The others are similar to those in the embodiment mode example 2.

In this example, effects similar to those in the embodiment mode example2 can be also obtained.

Embodiment Mode Example 4

A printed wiring board in accordance with an embodiment mode example ofa third invention will next be explained by using FIGS. 8 to 16.

As shown in FIG. 8, the printed wiring board 341 in this example has aninsulating substrate 305 constructed by two insulating layers 351, 352,a pad 301 for external connection arranged in an outermost layer of theinsulating substrate 305, conductor patterns 325, 326 arranged inanother layer different from the outermost layer, and holes 331, 332 forconductivity, electrically connecting the pad 301 for externalconnection and the conductor patterns 325, 326.

As shown in FIG. 9, the pad 301 for external connection closes anopening portion 339 on an outermost layer side of the hole 331 forconductivity and forms a bottom portion of the hole 331 forconductivity. An inner wall and the bottom portion of the hole 331 forconductivity are covered with a metallic plating film 323.

As shown in FIG. 15, an external connecting terminal 310 is joined to asurface of the pad 301 for external connection in a central position ofthe hole 331 for conductivity. The external connecting terminal 310 is asoldering ball for joining the printed wiring board 341 to a partnermember 308 such as a mother board, etc.

The pad 301 for external connection has a diameter A from 0.2 to 0.4 mm.An opening diameter B of the hole 331 for conductivity is approximatelyequal to a diameter from 0.1 to 0.3 mm.

In the insulating substrate 305, a mounting portion 370 for mounting anelectronic part 307 is formed in an outermost layer on a side opposed toan arranging side of the pad 301 for external connection. The mountingportion 370 is arranged approximately on the entire surface of a lowerportion of the electronic part 370. The electronic part 307 is adheredto the mounting portion 370 by an adhesive 372 such as silver paste,etc. Many bonding pads 327 for joining the bonding wire 371 are arrangedaround the mounting portion 370.

Surfaces of the respective insulating layers 351, 352 are covered with asolder resist 306. Inner walls and bottom portions of the holes 331, 332for conductivity are covered with the metallic plating film 323. Oneportion of the solder resist 306 enters the interiors of the holes 331,332 for conductivity.

A manufacturing method of the above printed wiring board will next beexplained.

First, an insulating layer constructed by a glass epoxy substrate isprepared. Next, as shown in FIG. 10, an upper face copper foil 321 and alower face copper foil 322 are respectively stuck to upper and lowerfaces of the insulating layer 351.

Next, as shown in FIG. 11, a portion of the upper face copper foil 321corresponding to a forming portion 338 of a hole for conductivity isremoved from the upper face copper foil 321 by etching so that anopening hole 328 is formed.

Next, a laser beam 388 is irradiated to the forming portion 338 of thehole for conductivity from above the upper face copper foil 321. Thus,as shown in FIG. 12, the hole 331 for conductivity is formed in theinsulating layer 351 exposed from the opening hole 328 of the upper facecopper foil 321, and a bottom portion of the hole 331 for conductivityis set to reach the lower face copper foil 322.

Next, as shown in FIG. 13, a metallic plating film 323 is formed in aninner wall and the bottom portion of the hole 331 for conductivity by achemical plating method and an electric plating method.

As shown in FIG. 9, this metallic plating film 323 is also formed on asurface of the lower face copper foil 322.

Next, the upper face copper foil 321 and the lower face copper foil 322are etched and a conductor pattern 325 electrically connected to thehole 331 for conductivity is formed from the upper face copper foil 321as shown in FIG. 14. Further, a pad 301 for external connection forclosing an opening portion of the hole 331 for conductivity is formedfrom the lower face copper foil 322.

Next, as shown in FIG. 9, a surface of the insulating layer 351 iscovered with a solder resist 306 and one portion of the solder resist306 enters the interior of the hole 331 for conductivity and fills thisinterior.

Next, as shown in FIG. 8, another insulating layer 352 is laminated withan upper face of the insulating layer 351 so that an insulatingsubstrate 305 is obtained. Specifically, a prepreg and a copper foil arelaminated and press-attached to the upper face of the insulating layer351. Next, the copper foil is etched so that a conductor pattern 326, abonding pad 327 and a mounting portion 370 are formed. Next, a laserbeam is irradiated to the insulating layer 352 so that a hole 332 forconductivity is formed. At this time, a bottom portion of the hole 332for conductivity is set to reach the internal conductor pattern 325.Next, a metallic plating film 323 is formed in an inner wall and thebottom portion of the hole 332 for conductivity by the chemical platingmethod and the electric plating method.

Next, a surface of the insulating layer 352 is covered with a solderresist 306, and one portion of the solder resist 306 enters the interiorof the hole 332 for conductivity and fills this hole. At this time, thebonding pad 327 is exposed as it is.

Thus, a printed wiring board 341 is obtained.

An operation and effects of the printed wiring board in this examplewill next be explained.

As shown in FIG. 8, the pad 301 for external connection is arranged soas to form a bottom portion of the hole 331 for conductivity. Therefore,it is unnecessary to form a conductor pattern for connecting the hole331 for conductivity and the pad 301 for external connection.Accordingly, a surplus area is formed on a surface of the insulatingsubstrate 305 and another conductor pattern, etc. can be arranged inthis surplus area so that high density surface mounting can be realized.Further, as shown in FIG. 15, the distance between the respective holes331 for conductivity can be reduced so that the holes 331 forconductivity can be arranged at high density in comparison with theconventional holes for conductivity.

As shown in FIG. 9, the pad 301 for external connection closes anopening portion of the hole 331 for conductivity on its outermost layerside and forms the bottom portion of the hole 331 for conductivity.Therefore, the pad 301 for external connection has at least an area ofthe opening portion of the hole 331 for conductivity. Hence, the pad 301for external connection can secure a sufficient joining area for joiningan external connecting terminal 310 and has an excellent joiningstrength to the external connecting terminal 310.

Further, a metallic plating film 323 for continuously covering an innerwall and a bottom portion of the hole 331 for conductivity is formedwithin the hole 331 for conductivity. Therefore, the pad 301 as thebottom portion for external connection is strongly joined to themetallic plating film 323 so that joining strength to the hole 331 forconductivity is improved. Hence, the pad 301 for external connection canbe reduced to a size close to that of the opening portion of the hole331 for conductivity. Accordingly, it is possible to obtain high densitymounting of the pad 301 for external connection and increase density ofsurface mounting of the insulating substrate 305.

In the manufacturing method of the above printed wiring board, as shownin FIGS. 13 and 14, after the metallic plating film 323 is formed in theinner wall and the bottom portion of the hole 331 for conductivity, thepad 301 for external connection is formed by etching the lower facecopper foil 322.

Therefore, the lower face copper foil 322 is closely attached stronglyto the metallic plating film 323 in the bottom portion of the hole 331for conductivity. Accordingly, the pad 301 for external connection canbe reduced to a size approximately equal to that of the hole 331 forconductivity so that high density mounting can be obtained.

As shown in FIG. 11, a laser beam 388 is irradiated to a forming portion338 of the hole for conductivity in an insulating layer 351. At thistime, the laser beam 388 gives high energy to the insulating layer 351so that a hole is sequentially bored within the insulating layer 351.When an end tip of the laser beam 388 reaches the lower face copper foil322, the laser beam 388 is reflected on the lower face copper foil 322.Therefore, when the irradiation of the laser beam 388 is stopped here, anon-through hole 331 for conductivity is formed as shown in FIG. 12. Inthis non-through hole 331 for conductivity, one opening portion 339 iscovered with the lower face copper foil 322 and no hole 331 extendsthrough the lower face copper foil 322.

It is here noticeable that the non-through hole can be formed byirradiating the laser beam 388. It is conventionally necessary that ahole is bored by a drill in the insulating layer and an opening portionof this hole is then covered with a copper foil to form such anon-through hole. However, the non-through hole reaching the lower facecopper foil 322 can be formed by irradiating the laser beam so that nocovering work of the opening portion is required after the boring.Therefore, the number of manufacturing processes is reduced andmanufacturing cost can be reduced.

The laser beam is also used when the hole 332 for conductivity is formedin another insulating layer 352. Therefore, it is possible to easilyform the hole 332 for conductivity in which the bottom portion of thehole 332 for conductivity reaches the internal conductor pattern 325.

The conductor pattern 325 formed on an upper face of the insulatinglayer 351 and the pad 301 for external connection formed on a lower faceof the insulating layer 351 can be simultaneously formed by etching theupper face copper foil 321 and the lower face copper foil 322.Therefore, the printed wiring board 341 can be manufactured easily andefficiently.

As mentioned above, it is possible to cope with the high densitymounting of the hole 331 for conductivity and the pad 301 for externalconnection. Therefore, as shown in FIG. 16, the conductor pattern 326connected to the bonding pad 327 is led around the interior of themounting portion 370 so that a chip size package having approximatelythe same size as the electronic part 307 can be obtained. In this case,it is necessary to secure an insulating property with respect to themounting portion 370 in the conductor pattern 326 led into the mountingportion 370. The mounting portion 370 is arranged approximately on theentire face of a lower portion of the electronic part 307 in aleading-in state of the conductor pattern 326.

Embodiment Mode Example 5

This example is an embodiment mode example of the third invention. In aprinted wiring board 342 in this example, the insulating substrate 305is constructed by a single insulating layer 351 as shown in FIG. 17.

A surface of the insulating layer 351 forms an outermost layer of theinsulating substrate 305. An electronic part 307 is mounted onto oneside of the insulating layer 351 and a soldering ball 310 is joined tothe other side of the insulating layer 351.

The other constructions are similar to those in the embodiment modeexample 4.

Effects similar to those in the embodiment mode example 4 can be alsoobtained in this example.

Embodiment Mode Example 6

A manufacturing method of a printed wiring board in an embodiment modeexample of a fourth invention will be explained by using FIGS. 18 to 27.

As shown in FIGS. 18 to 20, the printed wiring board 403 manufactured inthis example has a mounting portion 406 for mounting electronic partsand a conductor pattern 401 on the surface of an insulating substrate407. Further, a through hole 405 for performing electric conductionbetween upper and lower portions of the printed wiring board is formed.

The conductor pattern 401 is constructed by a land 411 of the throughhole 405, a terminal 413 for joining a bonding wire 461 connected to anelectronic part 60, a wiring circuit 412 for electrically connecting theland 411 and the terminal 413 to each other, and a pad 414 for joining asoldering ball 4.

Many through holes 405 are formed in a peripheral portion of theinsulating substrate 407.

The manufacturing method of the printed wiring board in this examplewill be explained next.

First, as shown in FIG. 21, an insulating substrate 407 constructed by aglass epoxy substrate is prepared, and a copper foil 415 is stuck toboth faces of the insulating substrate 407. Next, as shown in FIG. 22,an unnecessary portion of the copper foil 415 is removed therefrom byetching and a conductor pattern 401 is formed. Further, a plating lead402 for electrically connecting each conductor pattern 401 is formed. Aminimum clearance of the conductor patterns 401 interposing the platinglead 402 is set to 0.3 mm therebetween.

Next, as shown in FIG. 23, a through hole forming portion 450 of theinsulating substrate 407 is bored by using a drill, a router, etc. sothat a through hole 405 is bored.

Next, a chemical plating film 416 is formed on a surface of theconductor pattern 401 and is also formed in an inner wall of the throughhole 405. The chemical plating film 461 is made of copper and has 2 μmin thickness. Next, as shown in FIGS. 24 and 25, an electric current 404flows to the conductor pattern 401 and the chemical plating film 416through the plating lead 402 in a state in which the insulatingsubstrate 407 is dipped into an electric plating reservoir. Thus,surfaces of the conductor pattern 401 and the chemical plating film 416are covered with an electric plating film 417. The electric plating film417 is made of copper and has 10 μm in thickness.

Next, as shown in FIG. 26, a laser beam 408 is irradiated to the platinglead 402 so that the plating lead 402 is melted and cut. The laser beam408 is irradiated by using an excimer laser having 248 nm in wavelengthand 50 W in output. Thus, as shown in FIG. 27, the conductor patterns401 are insulated from each other.

Thus, a printed wiring board 403 shown in FIGS. 18 to 20 is obtained.

An operation and effects of this example will next be explained.

The laser beam is coherent light having aligned phases in order thatdirectivity is high. Accordingly, as shown in FIG. 26, high energy canbe given to a very small portion by irradiating the laser beam 408.Therefore, only the plating lead 402 can be melted and cut withoutdamaging the conductor pattern 401 even when the plating lead 402 isfinely constructed. Accordingly, the plating lead 402 can be formed in avery small pattern so that the distance between conductor patterns 401and the distance between through holes 405 can be reduced. Accordingly,high density mounting of the conductor patterns 401 can be realized inaccordance with this example.

INDUSTRIAL APPLICABILITY

As mentioned above, in accordance with the present invention, it ispossible to provide a printed wiring board capable of forming aninsulating film having a very small opening portion and a manufacturingmethod of the printed wiring board.

Although embodiments and examples of the invention have been shown anddescribed, it is to be understood that various modifications,substitutions, and rearrangements of parts, components, and processsteps, as well as other methods for preparing the printed wiring boardof the invention can be made by those skilled in the art withoutdeparting from the novel spirit and scope of the invention.

1. A manufacturing method of a printed wiring board in which a conductorpattern is formed on an upper face of an insulating layer and a pad forexternal connection is formed on a lower face of the insulating layer,and said conductor pattern and the pad for external connection areelectrically connected to each other by a hole for conductivity; themanufacturing method being characterized in that: an upper face copperfoil and a lower face copper foil are first respectively stuck to theupper and lower faces of the insulating layer; an opening hole is nextformed by removing a portion corresponding to a forming portion of thehole for conductivity in said upper face copper foil by etching; thehole for conductivity is next formed in the insulating layer exposedfrom the opening hole of said upper face copper foil, and a bottomportion of the hole for conductivity is set to reach said lower facecopper foil; a chemical plating film is next formed in an inner wall ofthe hole for conductivity; an electric plating film for continuouslycovering the inner wall and the bottom portion of the hole forconductivity is next formed within the hole for conductivity; aconductor pattern electrically connected to said hole for conductivityis next formed from the upper face copper foil by etching said upperface copper foil and the lower face copper foil, and a pad for externalconnection for closing an opening portion of said hole for conductivityis formed from said lower face copper foil.
 2. The manufacturing methodof the printed wiring board as claimed in claim 1, wherein one, two ormore other insulating layers are laminated with said insulating layerhaving the pad for external connection in a state in which said pad forexternal connection is arranged in an outermost layer after saidconductor pattern and the pad for external connection are formed.
 3. Themanufacturing method of the printed wiring board as claimed in claim 1,wherein an external connecting terminal is joined to a surface of saidpad for external connection in a central position of the hole forconductivity.
 4. The manufacturing method of the printed wiring board asclaimed in claim 2, wherein an external connecting terminal is joined toa surface of said pad for external connection in a central position ofthe hole for conductivity.